GSI Commerce, a company that powers e-commerce platforms for major brands, has acquired Retail Convergence, which operates RueLaLa.com, a private sale site and SmartBargains.com, an off-price e-commerce marketplace, in a deal valued as high as $350 million.

Launched in April 2008, RueLaLa is a members-only online sample sale that sells luxury brands at discount prices during two-day private sale events in the fashion, accessories, footwear, home, jewelry and other categories. SmartBargains.com, which launched in 1999, is a online marketplace for the sale of off-price merchandise across a wide cross-section of categories.

It’s not surprising that GSI wants to enter the online private sale space considering the growth of the other players in the same arena, such as Gilt Groupe,Vente Privee, HauteLook and Ideeli.

RueLaLa’s membership has already grown to more than 1.2 million members in 18 months and is seeing strong revenue growth. In the third quarter of 2009, RueLaLa’s net revenues increased by nearly five times from the previous year, to $28 million.